E764  Resolutio facilis quaestionis difficillimae, qua haec formula maxime generalis vvzz(axx+byy)^{2} + Δxxyy(avv+bzz)^{2} ad quadratum reduci postulatur
(An easy resolution to a most difficult question, where this most general form vvzz(axx+byy)^{2} + Δxxyy(avv+bzz)^{2} is required to be reduced to a square)
Summary:
Euler considers quadratic forms axx + 2bxy + cyy, a little more general than his usual form.
Biquadratic forms didn't seem to take off, though.
Publication:

Originally published in Memoires de l'academie des sciences de St.Petersbourg 9, 1824, pp. 1419

Opera Omnia: Series 1, Volume 5, pp. 71  76
 Reprinted in Commentat. arithm. 2, 1849, pp. 414417 [E764a]
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